It is generally thought that the carcinogens in tobacco smoke are primarily polynuclear aromatic hydrocarbons (PAHs), with benzo(a)pyrene and dibenzanthracene being particularly recognized examples. In fact, these two compounds are among the most carcinogenic substances found in tobacco smoke. Filters for removing PAHs from tobacco smoke have been proposed, and are exemplified by U.S. Pat. No. 3,828,801 to Merrill and U.S. Pat. No. 4,038,992 to Ogasa et al, the disclosures of which are incorporated herein by reference. However, this type of prior art proposes filters that would appear to be either expensive to produce or to lack selectivity for PAHs. The Ogasa et al patent uses, inter alia, a granular composition that is a blend of protein powder and active charcoal granules, whereas the Merrill patent proposes polysiloxane compositions mixed with the tobacco and/or employed in a filter.
There have been proposed in the prior art tobacco smoke filters containing additives such as coffee or tea for various stated purposes. U.S. Pat. No. 253,296 to Kinney, U.S. Pat. No. 2,172,946 to Sutter and U.S. Pat. No. 3,319,630 to Orrmins are illustrative. Coffee and tea contain caffeine, a purine, as well as a number of other organic compounds such as tannic acid. In the Kinney patent, cotton or other like filamentous material is saturated with a paste of one or more additive substances "having chemical properties which cause it to take up, neutralize, or destroy the nicotine, thus purifying the smoke and rendering it innoxious and pleasant," or if the additive substance is granulated, the filter may be made of a proper quantity of the additive substance united together by a suitable cement or gum. Examples of additive substances are given as charcoal, tea, coffee, benzoic acid, arsenic of soda, lichen from Iceland, and balsam of toln. The Sutter patent proposes ground or shredded roasted coffee or tea or an extract thereof as the sole or principal element in an absorbent and purifying composition that is used to "depoison" tobacco smoke. Sutter's stated purpose is to neutralize, paralyze or render harmless the noxious gases contained in tobacco smoke and to filter out certain other products of combustion, and he states that the caffeine or theine of roasted coffee or tea neutralizes the acid gases in the smoke, while the tannic acid neutralizes the alkaloid gases. The Orrmins patent relates to a tobacco smoke filter that contains a filter pack of dehydrated coffee or tea extract, which is said to have a high percentage content of concentrated and free tannin or tannic acid to neutralize the nicotine carried by tobacco smoke. In this type of prior art, there was and is no recognition that a purine such as caffeine will form a complex with and thereby selectively remove from tobacco smoke highly carcinogenic PAHs, or that a purine exerts a remarkably increased PAH-removing effect when used in combination with a filtering material having a particular capability for the removal of a certain amount of the total particulate matter (TPM) from smoke. This particular capability is discussed in detail below. Furthermore, to the extent that caffeine would be present in these proposed arrangements, it would be bound, complexed or masked as a minor constituent of coffee or tea, rather than free and uncomplexed caffeine. As such, it is believed that the caffeine would be masked by the other coffee constituents such that there would be very limited contact of the smoke with any caffeine present. Additional prior art similar to the three patents just discussed is Wynder and Hoffmann, "Tobacco and Tobacco Smoke," Academic Press, 1967, which mentions the use of roasted coffee granules and of tea leaves as a filter material for tobacco smoke at page 564 thereof. Also known in the prior art is the use of coffee and cocoa as tobacco blend additives. Exemplary of this type of prior art are U.S. Pat. No. 250,740 to Lawrence, and U.S. Pat. No. 1,927,984 to Krensky et al.
Research has shown that there is a selectively enhanced solubility of aromatic hydrocarbons such as the PAHs in aqueous solutions of purines such as caffeine. This type of prior art is illustrated by Brock et al, Arch. Exptl. Pathol. Pharmokol., 189:709 (1938); Wanless et al, Anal. Chem., 23:563 (1951); and Booth et al, Biochem. Biophys. Acta., 12:75 (1953). Furthermore, studies have been made of the bonding forces between PAHs such as pyrene and a purine such as 1,3,7,9-tetramethyluric acid, as illustrated by De Santis et al, Nature, 191:900 (1961). In addition, the prior art has shown that the oral administration of benzo(a)pyrene in rats markedly increases the rate of plasma clearance of caffeine; and that caffeine and to a lesser extent theophylline inhibits the binding of dimethyl benz(a)anthracene to mouse epidermal cell DNA in culture. The binding of this PAH to DNA appears to be a prerequisite for the initiation of its bioactivity. Prior art of this type is exemplified by Welch et al, Clin. Pharmacol. Ther., 22:791 (1977) and Shoyab, Arch. Biochem. Biophys., 196:307 (1979). Moreover, it has been shown that caffeine inhibits the carcinogenic action of cigarette smoke condensate fractions when added to the fractions prior to application on mouse skin. This type of art is illustrated by Rothwell, Nature, 252:69 (1974).
I am aware of no prior art or earlier work which discloses or suggests the remarkable capabilities of a purine-containing filter, especially a caffeine-containing particular filter, in removing PAH carcinogens from smoke, especially tobacco smoke.